I might face a similar issue with a Dell u2723qe. In my case it might be related to MST/Daisychaining: See here for more information:
https://www.dell.com/community/en/conversations/monitors/u2723qe-is-flickering-as-soon-as-dp-out-is-connected-on-macos/65037e8fa4619d31670bd914
maxammann_work
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